Method for removing reactive metal from a reactor system

ABSTRACT

A method for reducing catalyst contamination in a hydrocarbon conversion reactor system, comprising the steps of contacting at least a portion of a metal-coated hydrocarbon conversion reactor system comprising a reactive metal with a getter to produce a movable metal; and fixating the movable metal.

This is a division of application no. 08/781,434, filed Jan. 10, 1997,now U.S. Pat. No. 6,419,986.

FIELD OF THE INVENTION

The invention is a method of removing reactive metal from at least aportion of a metal-coated hydrocarbon conversion reactor system, so thatthe reactive metal does not deactivate the hydrocarbon conversioncatalyst. It is especially applicable to catalytic reforming processesusing halided catalysts.

BACKGROUND AND RELEVANT REFERENCES

Platinum L-zeolite catalysts for low-sulfur reforming were invented inthe early 1980's. After about 10 years of intensive effort, and muchresearch, low sulfur reforming was commercialized in the early 1990's.Progress toward commercialization required many discoveries. Two keydiscoveries were the criticality of ultra-low sulfur levels in the feed,and the impact of these ultra-low sulfur levels on reactor metallurgy,i.e., the discovery of the need to prevent coking, carburization andmetal dusting. A preferred way to prevent coking, carburization andmetal dusting utilizes a metal protective layer, especially onecomprising tin.

While commercialization of ultra-low sulfur reforming was being pursued,a second generation of sulfur-sensitive platinum L-zeolite catalystswere being developed. These new catalysts are halided. They allowoperations at higher severity, tolerate a wide range of hydrocarbonfeeds, have high activity and long life.

Recent attempts to utilize this second generation of catalysts forultra-low sulfur reforming resulted in an unexpected and undesiredreduction in catalyst activity. After much research and experimentation,it was discovered that the catalyst had been partially poisoned by themetal of the protective layer specifically by tin; which had been usedto prevent carburization and metal dusting of the reactor systemsurfaces. Somehow, some of this tin had migrated and deposited on thecatalyst. In contrast, when conventional platinum L-zeolite catalystsare used for ultra-low sulfur reforming in a tin-coated reactor system,neither tin migration nor catalyst deactivation due to tin migration areobserved. The cause of these problems has now been traced to low levelsof volatile hydrogen halides that, under certain conditions, evolve fromthe catalysts themselves. These halides interact with reactive tin andcan deactivate the catalyst.

Therefore, one object of the present invention is to reduce catalystdeactivation by metals derived from a metal-coated reactor system.Another object of the invention is to reduce catalyst contamination froma freshly metal-coated reactor system which would otherwise result incatalyst deactivation. This new process will also improve thereproducibility of catalytic operations, since catalyst activity andlife can be better predicted.

The use of metal coatings and metal protective layers, especially tinprotective layers, in hydrocarbon conversion processes is known. Theselayers provide improved resistance to coking, carburization and metaldusting, especially under ultra-low sulfur conditions. For example,Heyse et al., in WO 92/1856 coat steel reactor systems to be used forplatinum L-zeolite reforming with metal coatings, including tin. Seealso U.S. Pat. Nos. 5,405,525 and 5,413,700 to Heyse et al. Metal-coatedreactor systems are also known for preventing carburization, coking andmetal dusting in dehydrogenation and hydrodealkylation processesconducted under low sulfur conditions; see Heyse et al., in U.S. Pat.No. 5,406,014 and WO 94/15896. In the '014 patent, Example 3 shows theinteraction of a stannided coupon with hydrocarbons, methyl chloride andhydrogen at 1000 and 1200° F. The coupon was stable to methyl chlorideconcentrations of 1000 ppm at 1000° F., showing that the tin coating isstable to halogens at reforming temperatures.

The use of catalysts treated with halogen-containing compounds forcatalytic reforming is also known. See, for example U.S. Pat. No.5,091,351 to Murakawa et al. Murakawa prepares a Pt L-zeolite catalystand then treats it with a halogen-containing compound. The resultingcatalyst has a desirably long catalyst life and is useful for preparingaromatic hydrocarbons such as benzene, toluene and xylenes from C₆-C₈aliphatic hydrocarbons in high yield. Other patents that disclosehalided L-zeolite catalysts include U.S. Pat. Nos. 4,681,865, 4,761,512and 5,073,652 to Katsuno et al.; U.S. Pat. Nos. 5,196,631 and 5,260,238to Murakawa et al.; and EP 498,182 (A).

None of these patents or patent applications disclose any problemsassociated with the metal-coated reactor systems. They neither teach thedesirability nor the need for removing metal from the reactor system,especially not prior to catalyst loading or prior to hydrocarbonprocessing.

Indeed, the art teaches the advantages of combining one of the preferredcoating metals—tin—with a reforming catalyst, specifically with aplatinum L-zeolite catalyst. U.S. Pat. No. 5,279,998 to Mulaskey et al.,teaches that activity and fouling rate improvements are associated withtreating the exterior of the platinum L-zeolite catalyst with metallictin particles having an average particle size of between 1 and 5 microns(tin dust). For example, Table I of the Mulaskey patent shows improvedcatalyst performance when metallic tin dust is combined with a platinumL-zeolite catalyst that has been treated with fluoride according to theprocess of U.S. Pat. No. 4,681,865.

In light of the above teachings, we were surprised to find a decrease incatalyst activity upon reforming in a freshly tin-coated reactor systemusing a halided platinum L-zeolite catalyst. (See Example 5 below.)

Tin-coated steels are known to be useful for a variety of purposes. Forexample, surface coating compositions, known as stop-offs or resists,are temporarily applied to portions of a steel tool surface to shieldthem during case hardening. For example, in U.S. Pat. No. 5,110,854 toRatliff the stop-off is a water-based alkyd resin containing tin andtitanium dioxide.

It is also known that reacting tin with steel at elevated temperaturesresults in coated steels having surface iron stannides. Aside fromhydrocarbon processing, as discussed above, coated steels have been usedin applications where steels with hard and/or corrosion resistantsurfaces are desired. For example, Caubert in U.S. Pat. No. 3,890,686describes preparing mechanical parts having coatings consisting of threeiron stannides to increase the resistance of these parts to seizing andsurface wearing. In Example 2, a piece of coated steel is prepared byheating the steel to 1060° F. in the presence of tin chloride (SnCl₂)and hydrogenated nitrogen for 1.5 hours.

It is also known to treat tin-coated steels to further modify theirproperties. For example, Galland et al., in U.S. Pat. No. 4,015,950teach that hot dipping stainless steel into molten tin results in twointermetallic stannide layers, an outer FeSn layer and inner layer whichcomprises a mixture of Fe (Cr,Ni,Sn) and FeSn₂. The inner layer has agreater hardness. They teach that the outer layer can be removed bygrinding, by reacting with 35% nitric acid containing a polyamine, or byelectrochemical means, leaving behind the harder and more corrosionresistant inner layer.

Another example where tin-coated steel is modified is Carey II, et al.,in U.S. Pat. No. 5,397,652. Here, tin-coated stainless steels are taughtas roofing materials and siding, especially for use in marine or salineenvironments. Carey II, et al. teach that hot-dipping stainless steelinto molten tin results in a bonded tin coating and an underlyingintermetallic alloy of chromium-iron-tin. They teach treating the coatedsteel with an oxidizing solution (aqueous nitric acid) to obtain auniformly colored stainless steel. The nitric acid preferentially reactswith the bonded tin coating leaving behind the uniformly coloredintermetallic alloy. None of these patents on coated steels areconcerned with hydrocarbon conversion processing.

None of the art described above is concerned with the problemsassociated with reactive metals derived from metal coatings, such as tincoatings, nor with the effect of these reactive metals on catalysts,especially platinum L-zeolite reforming catalysts.

We have discovered that there are problems associated with usingmetal-coated reactor systems—especially freshly-coated systems—in thepresence of certain catalysts, and we have discovered the cause of andsolutions for these problems. Thus, one object of the present inventionis to reduce catalyst contamination from a freshly metal-coated reactorsystem. Another object of the invention is to ensure that catalystcontamination is avoided, for example when replacing a conventionalcatalyst with a halided catalyst.

SUMMARY OF THE INVENTION

In one embodiment, the invention is a method of removing reactive metalfrom at least a portion of a metal-coated reactor system that is usedfor converting chemicals, especially hydrocarbons. The method comprisescontacting at least a portion of a reactor system containing reactivemetal with a getter to produce movable metal, and fixating the movablemetal, the getter, or both. The getter reacts with the reactive metal(derived from the coating metal) facilitating its removal from thereactor system. Preferably the movable metal and the getter are bothfixated, for example by trapping using a solid sorbent.

Preferred metal coatings are those prepared from tin-, germanium-,antimony-, and aluminum-containing compositions. More preferably, thereactive metal comprises a tin-containing composition includingelemental tin, tin compounds or tin alloys.

Preferably the getter is prepared from a gaseous halogen-containingcompound; more preferably the getter comprises a hydrogen halide,especially HCl prepared in-situ. In a preferred embodiment, a conversioncatalyst is then loaded into the reactors after the reactive metal isremoved, and conversion operations begin.

In another embodiment, the invention is a method of removing reactivetin from at least a portion of a reactor system having freshly-stannidedsurfaces. The method comprises the steps of:

a) applying a tin plating, paint, cladding or other coating to airon-containing base substrate portion of a reactor system;

b) heating the coated substrate at temperatures greater than 800° F.,preferably in the presence of hydrogen to produce a reactor systemhaving freshly-stannided surfaces and which contains reactive tin;

c) removing at least a portion of the reactive tin from the reactorsystem by contacting the reactive tin with a getter to produce movabletin; and

d) sorbing or reacting the movable tin.

Preferably, the reactive tin is removed by contacting the surfaceportion with a gaseous halogen-containing compound, such as HCl. Ingeneral, the contacting is done at temperatures and flow ratessufficient to transport a significant amount of the movable tin out ofthe reactor and furnace tubes and onto a sorbent. Here again it ispreferred that the method be conducted prior to catalyst loading.

In yet another embodiment, the invention is a method for reducingcatalyst contamination from a metal which was used to coat a reactorsystem. The method comprises contacting a metal-coated reactor systemprior to catalyst loading with a getter, preferably a gaseoushalogen-containing compound, to produce movable metal; and removing andfixating at least a portion of the movable metal from the reactorsystem. The conversion catalyst is then loaded into the reactor system,and conversion operations begin with feed being converted to product inthe reactor system. This method is preferably applied to afreshly-coated reactor system.

In yet another embodiment, the invention is a catalytic reformingprocess. The process comprises removing reactive tin from a tin-coatedreforming reactor system by contacting a tin-coated reactor system witha halogen-containing compound to produce movable tin; mobilizing andsorbing the movable tin; loading a halided Pt L-zeolite catalyst intothe reactor system; and reforming hydrocarbons to aromatics.

Among other factors, this invention is based on our observation thathalided Pt L-zeolite catalysts are partially deactivated during thestart-up phase of a catalytic reforming process, especially when thestart-up is done in a freshly tin-coated reactor. This is in contrast towhat is observed with conventional Pt L-zeolite catalysts (which are nothalided); here catalyst deactivation due to a tin coating has not beennoted.

The art appears to be totally silent about the presence of reactivemetal in metal-coated hydrocarbon conversion reactor systems. Moreover,the art has not appreciated the need or desire to remove this reactivemetal prior to catalyst loading, especially prior to loading halidedcatalysts. We have found that tin-coated reactor systems, especiallythose with freshly prepared tin intermetallics, can lose tin from thetin-coated surfaces when contacted with halogen-containing gases, forexample, during the start-up of a reforming process using a halided PtL-zeolite catalyst which evolves acid halides, including HCl. This metalloss results in tin depositing on the catalyst and reduced catalystactivity.

However, we have observed that after several start-up cycles, catalystactivity stabilizes without significant further decline. Thus, webelieve that a reactive tin is present in the freshly-coated reactors.When contacted with hydrogen halides (e.g., HCl and/or HF), this tin isunexpectedly mobilized and deactivates the platinum catalyst. Based onthese discoveries, we have developed simple, inexpensive procedures thatquickly and efficiently remove reactive tin from tin-coated reactorsystems, preferably prior to catalyst loading. When the catalyst is thenloaded into the reactors and hydrocarbon processing begins, the catalystexperiences little or no deactivation from the tin coating.

DESCRIPTION OF THE FIGURES

FIG. 1 shows HCl evolution (on right) from a halided reforming catalystas a function of temperature (on left). Hydrogen was added at 500° F. attime=79 hours.

FIG. 2 shows experimental configurations for screening tests describedin Examples 5 and 6.

FIG. 3 shows total tin weight loss from a stannided coupon as a functionof the number of startup cycles, each done in the presence of freshhalided Pt L-zeolite catalyst (open circles). The line at the bottom(closed circles) is a control. See Example 7.

DETAILED DESCRIPTION OF THE INVENTION

In one broad aspect, the present invention is a process for removingreactive metal from at least a portion of a metal-coated reactor system.This process comprises contacting at least a portion of a metal-coatedreactor system with a getter. Preferably the getter is ahalogen-containing compound, more preferably HCl. The getter convertsthe reactive metal to movable metal, which is fixated. Optionally, themovable metal is also mobilized, for example to another location in theprocess equipment, prior to being fixated.

In another embodiment, the invention is a method for reducing catalystcontamination from a metal which was used to coat a reactor system. Themethod comprises contacting a metal-coated reactor system prior tocatalyst loading with getter comprising a gaseous halogen-containingcompound to produce movable metal. The movable metal is then removedfrom the reactor system. In one especially preferred embodiment, theinvention is a method for reducing contamination of a Pt L-zeolitereforming catalyst by tin from a freshly tin-coated reactor systemhaving intermetallic stannides on the surfaces to be contacted withhydrocarbons.

Although the terms “comprises” or “comprising” are used throughout thisspecification, these terms are intended to encompass both the terms“consisting essentially of”, and “consisting of” in various preferredaspects and embodiments of the present invention.

As used herein, the term “reactor system” is intended to include the hotsections of chemical conversion units, especially hydrocarbon conversionunits. These units typically comprise one or more conversion reactorsand one or more furnaces comprising a plurality of furnace tubes to heatthe feed. The term “reactor system” is also intended to include unitscomprising furnace tube reactors where conversion occurs in furnacetubes (i.e., inside the furnace). The “hot sections” of these units arethose sections where the feed is at or above the reaction or processtemperature, and/or where the hydrocarbon conversion reactions occur.

As used herein, the term “metal-coated reactor system” is intended toinclude reactor systems (see above) having a metal-containing cladding,plating, paint or other coating, applied to at least a portion of thesurfaces that are to be contacted with hydrocarbons at or above processtemperature. Preferably at least half, more preferably at least threequarters, most preferably all of the surface area that is to becontacted with hydrocarbons at or above process temperature. The term“metal-coated reactor system” is also intended to include reactorsystems having protective layers, such as intermetallic layers that areprepared from claddings, platings, paints or coatings. Depending on themetal, a reactor system having a coating applied thereto may be cured byheating, preferably in a reducing environment, to produce intermetalliclayers. The metal-coated reactor system preferably comprises a baseconstruction material (such as a carbon steel, a chromium steel, or astainless steel) having one or more adherent metallic layers attachedthereto. Examples of metallic layers include elemental chromium,aluminized surfaces and iron-tin intermetallic compounds such as FeSn₂.Freshly-coated reactor systems, for example ones that have beenfreshly-stannided, are those which has not been used for hydrocarbonprocessing since coating, or since coating and curing.

As used herein, the term “metal-containing coating” or “coating” isintended to include claddings, platings, paints and other coatings whichcontain either elemental metals, metal oxides, organometallic compounds,metal alloys, mixtures of these components and the like. The metal(s) ormetal compounds are preferably a key component(s) of the coating.Flowable paints that can be sprayed or brushed are a preferred type ofcoating.

As used herein, the term “halogen-containing compound” or“halogen-containing gas” includes, but is not limited to, elementalhalogen, acid halides, alkyl halides, aromatic halides, other organichalides including those containing oxygen and nitrogen, inorganic halidesalts and halocarbons or mixtures thereof. Water may optionally bepresent.

As used herein, the term “reactive metal”, such as “reactive tin”, isintended to include elemental metals or metal compounds that are presenton metal-coated reactor system surfaces and that can be mobilized atprocess or furnace tube temperatures, for example in the presence ofdilute gaseous HCl, i.e., in the presence of between about 0.1 to about100 ppm HCl. For instance, reactive tin has been observed when a halidedcatalyst which can evolve HCl was used for catalytic reforming in afreshly tin-coated reactor system having freshly-prepared,intermetallic, stannide layers. When used in the context of reforming,the term “reactive tin” comprises any one of: elemental tin, tincompounds, tin intermetallics and tin alloys that will migrate attemperatures between 600-1250° F. when contacted with a getter, andwhich would thereby result in catalyst deactivation during reformingoperations or during heating of the reformer furnace tubes. In othercontexts, the presence of reactive metal will depend on the particularmetal, the getter, as well as the hydrocarbon conversion process and itsoperating conditions. Screening tests, as described in the examples, canbe modified for the particular metal and process of interest todetermine if reactive metal will be present during processing andtherefore cause problems.

The term “movable metal” or “movable tin” is also used herein. It refersto the reactive metal (e.g., tin) after reaction with the getter.Generally, it is the movable metal that is fixated.

Although discussed hereinafter in terms of providing tin-intermetalliclayers or tin coatings, it is believed that germanium-, arsenic- andantimony-intermetallic layers, especially freshly prepared layers alsocomprise reactive metal, and that our discoveries are also applicable tothese metals. The discussion herein of tin coating or tin-intermetalliclayers is merely intended to exemplify a preferred embodiment, and isnot intended to limit the invention to tin coatings or tinintermetallics.

Getters and Halogen Sources

The “getter” of this invention is any composition that will interactwith the reactive metal and facilitate its removal from the reactorsystem. Contacting the getter with the reactive metal converts it to aform that is movable and therefore can be removed from the reactorsystem, e.g., by a hot flowing gas. As will be appreciated by oneskilled in the art, the effectiveness of a getter will depend on thecontacting time and temperature, the getter concentration, theparticular reactive metal and its chemical and physical form.

Preferred getters are halogen-containing compounds or are prepared fromthese compounds. Useful getters comprise organic halides, includinghalocarbons, and inorganic halides, as well as inorganic halides,including metal halides and hydrogen halides. Some examples ofhalogen-containing compounds that are useful in this invention includeHCl, Cl₂MeCl, benzyl chloride, benzoyl chloride and NH₄Cl; HBr, Br₂,MeBr, benzyl bromide and; NH₄IHF, F₂, and MeF; HI, I₂, MeI, iodobenzene,and NH₄I; CCl₄, C₂Cl₄, C₂Cl₆, C₂H₂Cl₂, and CF₄, CF₃Cl, CF₂Cl₂, CFCl₃,CHFCl₂, CHF₂Cl, CHF₃, C₂F₂Cl₄, C₂F₄Cl₂ and C₂H₄F₂. Other useful organichalogen-containing compounds include those containing heteroatoms suchas oxygen and nitrogen, e.g., chloropyridine, acetoyl bromide and aminesalts of acid halides, e.g., pyridine hydrochloride. Other usefulgetters include metal halides such as SnCl₄, GeCl₄, SnHCl₃; transitionmetal halides such as iron chloride, chromium chloride, copper chloride,nickel chloride, etc., especially in their highest oxidation state; andhalided support materials or other solids which can produce HCl uponheating.

Preferred halogen-containing compounds are those that can readilyproduce HCl in situ; for example by reaction with hydrogen and a Ptcatalyst. These include C₂Cl₄, MeCl, and CCl₄. The most preferred gettercomprises a hydrogen halide, more preferably HCl. It is believed thatother volatile acids would also be effective getters, especially whenthe resulting movable metal (compound) is volatile at processtemperatures. The HCl can be provided as a gas; however, it is preferredto generate the HCl in-situ. This can readily be accomplished byreacting a halogen-containing compound such as perchloroethylene withhydrogen over a nickel or platinum catalyst, such as Raney nickel or aconventional Pt on alumina reforming catalyst, at elevated temperatures,for example at about 900° F.

The halogen-containing compounds are preferably present in diluteconcentration. Concentrations between about 0.1 and 1000 ppm arepreferred, more preferably between 1 and 500 ppm, most preferablybetween 10 and 200 ppm. The diluent preferably comprises hydrogen,especially when HCl is prepared in-situ. Preferably the hydrogen iscombined with an inert gas, such as nitrogen. For catalysts that areirreversibly poisoned by sulfur, such as non-acidic Pt L-zeolitecatalyst, it is important to use a halogen-containing gas that issubstantially free of sulfur, preferably one having less than 10 ppbsulfur. When HCl concentrations are too high, or temperatures are toohot, undesirable removal of the protective layers may occur, leaving theunderlying substrate (e.g., steel) susceptible to attack.

A preferred sulfur-free gas comprises nitrogen, and the processpreferably includes a step where a hydrogen-nitrogen gas mixture (e.g.,10% hydrogen in nitrogen) is used during the metal removal step. Forexample, a nitrogen and/or hydrogen stream can be spiked with smallamounts of getter.

While not wishing to be bound by theory, it is believed that, especiallyin a freshly-coated reactor system comprising surface intermetallics,there will be some metal that has not reacted with the base constructionmaterial. This unreacted coating metal is believed to be, at least inpart, the reactive metal that is removed in the process of thisinvention. For example, when iron and nickel stannides are produced bycuring/reduction of tin paints on steel, a fine tin-containing dust isobserved on the stannided surface. When examined by petrographicanalysis, the metal surface contains tiny microscopic tin balls whichare believed to be unreacted tin. Some of these balls appear to besitting on the intermetallic surface while others are connected to thesurface via what appears to be stannide roots. It is this unreacted tinthat we believe is removed by the process of this invention.

The amount of unreacted tin and tin dust that is present depends on avariety of factors. These include the thickness of the coating, the cureconditions that were used to prepare the stannides, and the type ofsteel or other base metallurgy to which the tin coating was applied. Theprocess of this invention removes a substantial portion of this dust andunreacted tin from the reactor system surfaces.

Alternatively, it is envisioned that the getter would transform thereactive metal into an inactive form. For example, the getter couldconvert the reactive metal to an immobile form, which effectivelyfixates it.

Fixating and Fixating Agents

Fixating the movable metal ensures that it will not deactivate thehydrocarbon conversion catalyst. The term “fixating” as used hereinmeans to purposely immobilize the metal or metal compounds produced fromthe reactive metal by the getter in order to reduce or prevent catalystcontamination. Fixating also refers to sorbing, reacting or otherwiseimmobilizing the getter. This fixating may be done using chemical orphysical treating steps or processes. The fixated metal may beconcentrated, recovered, or removed from the reactor system. Forexample, the movable metal may be fixated by contacting it with anadsorbent, by reacting it with compound that will immobilize the metal,or by dissolution, e.g., by washing the reactors system surfaces with asolvent and removing the dissolved movable metal. Solid sorbents arepreferred fixating agents.

In an especially preferred embodiment, a gas comprising HCl is used asthe getter. Then effluent HCl, residual halogen-containing gas (ifpresent) and movable metal, (e.g., in the form of SnCl₂) are all fixatedby sorption. The sorbent is a solid or liquid material (an adsorbent orabsorbent) which will trap the movable metal. Solid sorbents aregenerally preferred as they are easy to use and subsequently easy toremove from the system. The choice of sorbent or metal trap, depends onthe particular form of the movable metal and its reactivity. Suitableliquid sorbents include water, liquid metals such as tin metal, caustic,and other basic scrubbing solutions.

Suitable solid sorbents effectively immobilize the movable metal byadsorption or by reaction. The sorbent preferably has a high surfacearea (>10 m²/g), interacts strongly with the movable metal (has a highcoefficient of adsorption) or reacts with the movable metal toimmobilize the metal. The sorbent preferably retains its physicalintegrity after fixating the movable metal (e.g., has acceptable crushstrength, attrition resistance etc.). Suitable sorbents include metalturnings, such as iron turnings which will react with movable tinchloride. Preferred sorbents include aluminas, clays, silicas, silicaaluminas, activated carbon, and zeolites. A preferred sorbent is basicalumina, such as potassium on alumina, especially calcium on alumina.

The location of the sorbent is not critical. For example, it can belocated in one or more of the reactors, or preferably at or downstreamof the last reactor, or in a special knockout reactor. If the metalremoval process is done prior to catalyst loading, it is preferred toplace a solid sorbent at the bottom of the last reactor, or just priorto the heat exchangers. In this way, all surfaces that are contactedwith getter are located before the sorbent. If the removal process isdone with catalyst present, it is preferred to place solid sorbent onthe top of each reactor bed. In this instance, it is envisioned thatgetter would be injected near each furnace inlet and the movable metalwould be sorbed before reaching the catalyst beds. Here, a major portionof the coated surface would be contacted with the getter, and most ofthe reactive metal would be fixated.

The movable metal can be fixated simultaneously as it is reacted withthe getter or in one or more separate steps. For example, movable tin,such as tin chloride, can be formed at temperatures where tin chlorideis volatile, and the tin chloride is then immediately contacted with asolid sorbent. Alternatively, after contacting the reactive tin with HClat about 600° F., the reactor system can be cooled (e.g., to ambienttemperature) and produced metal halide (e.g., tin chloride) can then bemobilized and fixated by washing it out of the reactor system with wateror another suitable solvent. In another two-step process, tin chloridecan be produced on the reactor system surfaces at a first lowertemperature and then removed from the reactor system at a second highertemperature where tin chloride is volatile. The volatile tin chloride isthen fixated downstream or at the outlet of the reactor system.

The amount of fixating agent is not critical, so long as there is asufficient amount to fixate the movable metal, e.g., a sufficient amountof sorbent to sorb the desired amount of movable metal. Generally, it isalso advantageous to sorb any getter, such as HCl, present in thereactor effluent.

Ways to Remove Reactive Metal

There are a variety of ways to remove reactive metal from a metal-coatedreactor system. The method used and its effectiveness depends on thecoating metal and on the configuration and planned operations of thereactor system. For example, if the reactive metal is in the furnacetubes, these tubes can be temporarily connected in a loop, and a heatedsolution or gaseous composition containing getter can be circulatedthrough the loop. Here it is envisioned that the getter solution couldalso serve as the fixating agent. After sufficient contact time, itwould be drained or otherwise removed. Alternatively, if the movablemetal is formed as a gas, it can be fixated, e.g., by sorption, duringgas circulation.

If the reactive metal is located within a reactor, then it is preferredto remove this reactive metal by contacting the metal-coated surfaceswith a getter, preferably a halogen-containing gas at hydrocarbonconversion conditions. For example, a halided support material, such asa halided catalyst base (i.e., one free of catalytic metal) can beplaced in the first reactor, optionally along with a catalyst thatconverts halogen-containing compounds and hydrogen to HCl. The halidedcatalyst base can be prepared, for example, by impregnating NH₄Cl ontoalumina. Following typical catalyst start-up procedures, hydrogenhalides will evolve gradually from the halided catalyst base as thetemperature increases. This approach models conditions that will occurwhen catalyst is present. Here the coated reactor system is treated in amanner similar to that which will occur when catalyst is present.

It is preferred that prior to contacting the reactor system with thegetter, the coated reactor system is visually inspected, and wherepractical, any observed excess metal is manually removed. Care should betaken so that this physical removal does not result in portions of thereactor system being unprotected during hydrocarbon processing.

The metal removal step is preferably done in the absence of the processcatalysts and hydrocarbons. The metal-coated steel is contacted,preferably after curing, with a getter such as a HCl, preferably attemperatures and pressures similar to those at which the hydrocarbonconversion process will be operated. The metal removal step may remove aportion of the metal coating. However, the remaining coating issignificantly less susceptible to further metal loss, for example, insubsequent start-up cycles. Of course, it is important that asufficiently thick coating layer remain which is still effective for itsintended purpose, e.g., for preventing carburization, coking and metaldusting.

The metal removal process is continued until most of the reactive metalis removed. Preferably the removal is continued until the rate of metalremoval has declined substantially. For a freshly-coated reactor system,it is preferred that metal weight loss be measured every 10 hours. Theremoval process is continued until the rate of metal weight loss isabout 20% of the original rate of metal weight loss.

There are numerous ways to determine when to stop adding getter to thereactor system. Metal-coated, removable coupons can be used to determinewhen to discontinue adding getter. For example, small by-pass streamscan be provided near the furnace and/or the reactor. A section of theby-pass stream can be used to house the coated coupons. This sectionshould be able to be isolated from the other part of the by-pass streamby valves. During the metal removal process, these valves can be closedperiodically and coupons can be removed for inspection or to determinethe metal weight loss of the coupons. Actual metal weight loss curvesfor these coupons can be compared with the curve shown in FIG. 3. Themetal removal process can be ended after the metal weight loss hasleveled off, e.g., when the knee of the curve has been passed.

In commercial operations, a pre-test using coated coupons in a pilotplant can be used to determine a target metal weight loss. Given thistarget, removable coated coupons can be placed in the reactor system andweighed at intervals. When the target weight loss is achieved, the metalremoval process is discontinued. It is preferred that the pre-tests bedone at temperatures typical of the hottest portion of the reactorsystem.

Alternatively, visual or microscopic inspections of the reactor systemsurface can be used to determine when to stop adding getter in the metalremoval process. For example, the reactors can be opened and inspected.If tin dust is still present on the reactor surface, removal operationsare continued. If this dust is absent or has been converted to tinchloride (which is readily identified as it is water soluble), then theaddition of getter can be terminated.

Our data on tin weight losses over multiple startups suggests that asignificant portion of the reactive tin is removed relatively quickly,followed by a more gradual loss. See FIG. 3. Calculations show that thislater gradual loss would only deposit approximately 50 ppm tin on thecatalyst per start-up, which we expect will reduce catalyst activityonly slightly, by less than 1° F.

Platings, Claddings, Paints and Other Coatings

Metal coatings are typically applied to reactor systems to improveprocess operability. The reactor systems of this invention havegenerally had metallic protective layers applied to reduced coking,carburization and metal dusting.

The invention does not apply to all coating metals. Manymetal-containing platings, claddings, paints and coatings do not producereactive metals under conversion/process conditions. However, simpletests such as those described in the examples will readily identifymetals and coatings that require the metal removal process of thisinvention.

The metal used in the coating depends on the requirements of thehydrocarbon conversion process of interest, for example, itstemperatures, reactants, etc. Coating metals that melt below or atprocess conditions and form intermetallic complexes with the substratematerial are especially preferred. They are able to more readily providecomplete substrate coverage. These metals include those selected fromamong tin, antimony, germanium, arsenic, bismuth, aluminum, gallium,indium, copper, and mixtures, intermetallic compounds and alloysthereof. Preferred metal-containing coatings comprise metals selectedfrom the group consisting of tin, antimony, germanium, arsenic, bismuth,aluminum, and mixtures, intermetallic compounds and alloys of thesemetals. Especially preferred coatings include tin-, antimony-andgermanium-containing coatings. These metals will form continuous andadherent protective layers. Tin coatings are especially preferred—theyare easy to apply to steel, are inexpensive and are environmentallybenign. The most preferred metals interact with, or more preferablyreact with, the base material of the reactor system to produce acontinuous and adherent metallic protective layer at temperatures belowor at the intended hydrocarbon conversion conditions.

Metal-containing coatings that are less useful include certain metaloxide coatings such as those containing molybdenum oxide, tungsten oxideand chromium oxides. In part this is because it is difficult to formadherent metallic protective layers from these oxides at temperatureswhere hydrocarbon conversion equipment is operated.

It is preferred that the coatings be sufficiently thick that theycompletely cover the base metallurgy, and that after removal of themovable metal, the resulting protective layer remain intact, so it canprotect the steel for years of operation. At the same time, thin layersare desirable. Thin layers can be produced readily, are less costly thanthicker layers, and are less likely to fracture under thermal stress.Thus, the optimum thickness of the protective layer depends on theintended use conditions and the specific coating metal. For example, tinpaints may be applied to a (wet) thickness of between 1 to 6 mils,preferably between about 2 to 4 mils. In general, the thickness aftercuring is preferably between about 0.1 to 50 mils, more preferablybetween about 0.5 to 10 mils, most preferably about 1 mil. Also, it isdesirable that the coating and any produced intermetallic layers atleast initially be firmly bonded to the steel; this can be accomplished,for example, by curing at elevated temperatures. For example an appliedtin paint can be cured in hydrogen at 1100° F. for 24 hours.

Metal-containing coatings can be applied in a variety of ways, which arewell known in the art. These include electroplating, chemical vapordeposition, and sputtering, to name just a few. Preferred methods ofapplying coatings include painting and plating. Where practical, it ispreferred that the coating be applied in a paint-like formulation(hereinafter “paint”). Such a paint can be sprayed, brushed, pigged,etc. on reactor system surfaces.

Tin is a preferred coating metal and is exemplified herein; disclosuresherein about tin are generally applicable to other metals such asgermanium. Preferred paints comprise a metal component selected from thegroup consisting of: a hydrogen decomposable metal compound such as anorganometallic compound; a finely divided metal; and a metal oxide,preferably a metal oxide that can be reduced at process or furnace tubetemperatures. In a preferred embodiment a cure step is used to produce aintermetallic protective layer bonded to the steel through anintermediate bonding layer, for example a carbide-rich bonding layer.This is described in U.S. Pat. No. 5,406,014 to Heyse et al., which isincorporated herein by reference in its entirety.

Some preferred coatings and paint formulations are described in U.S.Ser. No. 803,063 to Heyse et al., corresponding to WO 92/15653, which isalso incorporated herein by reference in its entirety. One especiallypreferred tin paint contains at least four components or theirfunctional equivalents: (i) a hydrogen decomposable tin compound, (ii) asolvent system, such as isopropanol, (iii) finely divided tin metal and(iv) tin oxide. As the hydrogen decomposable tin compound,organometallic compounds such as tin octanoate or neodecanoate areparticularly useful. Component (iv), the tin oxide is a poroustin-containing compound which can sponge-up the organometallic tincompound, and can be reduced to metallic tin. The paints preferablycontain finely divided solids to minimize settling. Finely divided tinmetal, component (iii) above, is also added to insure that metallic tinis available to react with the surface to be coated at as low atemperature as possible. The particle size of the tin is preferablysmall, for example one to five microns. When tin paints are applied atappropriate thicknesses, heating under reducing conditions will resultin tin migrating to cover small regions (e.g., welds) which were notpainted. This will completely coat the base metal.

Cure Process Conditions

Some coating compositions need to be cured by heat treatment to producecontinuous and adherent protective layers. Cure conditions depend on theparticular metal coating as well as the hydrocarbon conversion processto which the invention is applied. For example, gas flow rates andcontacting time depend on the process configuration, the coating metalthe components of the coating composition, and the cure temperature.Cure conditions are selected to result in a continuous and uninterruptedprotective layer which adheres to the steel substrate. Cure conditionsmay be readily determined. For example, coated coupons may be heated inthe presence of hydrogen in a simple test apparatus; the formation of acontinuous protective layer may be determined using petrographicanalysis.

As discussed above, it is preferred to contact the metal-coated reactorsystem with the getter after the curing step, especially whenintermetallics are formed during heat treatment. Tin paints arepreferably cured between 900° F. and 1100° F.; germanium and antimonypaints are preferably cured between 1000° F. and 1400° F. Curing ispreferably done over a period of hours, often with temperaturesincreasing over time when the paint contains reducible oxides and/oroxygen-containing organometallic compounds. Reduction/curing ispreferably done using a gas containing hydrogen, more preferably in theabsence of hydrocarbons.

As an example of a suitable paint cure for a tin paint, the systemincluding painted portions can be pressurized with flowing nitrogen,followed by the addition of a hydrogen-containing stream. The reactorinlet temperature can be raised to 800° F. at a rate of 50-100° F./hr.Thereafter the temperature can be raised to 950-975° F. at a rate of 50°F./hr, and held for about 48 hours.

In a preferred embodiment the metal-coated reactor system comprises anintermetallic layer. This layer (which covers a base constructionmaterial such as a steel substrate) contains two or more metals, themetals being present in a stoichiometric ratio, i.e., as intermetalliccompounds. Intermetallic compounds are well known in the art; they aremore structured than molecular mixtures or alloys. Moreover, they havephysical properties (such as color) and chemical properties that areunique to the intermetallic phase.

For example, an intermetallic stannide layer contains tin intermetalliccompounds comprising tin and at least one other metal, the tin and theother metal(s) being present in compounds which have a stoichiometricratio of elements that vary only within a narrow range. Examples ofthese tin intermetallic compounds are Fe₃Sn, FeSn₂, Ni₃Sn₂, Ni₃Sn,Ni₃Sn₄. Other examples include mixed metal intermetallic stannides, forexample (Fe,Ni)_(x)Sn_(y) where Fe and Ni substitute freely for oneanother, but summed together are present in a stoichiometric ratio withthe tin.

The Base Construction Material

There are a wide variety of base construction materials to which theprocess of this invention may be applied. In particular, a wide range ofsteels and alloys may be used in the reactor system. In general, steelsare chosen so they meet minimum strength and flexibility requirementsneeded for the intended hydrocarbon conversion process. Theserequirements in turn depend on process conditions, such as operatingtemperatures and pressures. Additionally, the steel is chosen so it isnot susceptible to expected corrosion hazards.

Useful steels include carbon steel; low alloy steels such as 1.25, 2.25,5, 7, and 9 chrome steel with or without molybdenum; 300 seriesstainless steels including type 304, 316 and 347 stainless steel; heatresistant steels including HK-40, HP-50 and manurite, as well as treatedsteels, such as aluminized or chromized steels.

Conversion Processes

The invention is applicable to a variety of conversion processes whichuse catalysts to convert feed to products in metal-coated reactorsystems. In particular, the invention is applicable to hydrocarbonconversion processes that use catalysts which can be deactivated byreactive metal from the reactor system coating. Preferred hydrocarbonconversion processes include dehydrocyclization, especiallydehydrocyclization of C₆ to C₈ paraffins to aromatics; catalyticreforming; non-oxidative and oxidative dehydrogenation of hydrocarbonsto olefins and dienes; dehydrogenation of ethylbenzene to styrene and/ordehydrogenation of isobutane to isobutylene; conversion of lighthydrocarbons to aromatics; transalkylation of toluene to benzene andxylenes; hydrodealkylation of alkylaromatics to aromatics; alkylation ofaromatics to alkylaromatics; production of fuels and chemicals fromsyngas (H₂ and CO); steam reforming of hydrocarbons to H₂ and CO;production of phenylamine from aniline; methanol alkylation of tolueneto xylenes; and dehydrogenation of isopropyl alcohol to acetone. Morepreferred hydrocarbon conversion processes include dehydrocyclization,catalytic reforming, dehydrogenation, isomerization, hydrodealkylation,and conversion of light hydrocarbon to aromatics, e.g., Cyclar-typeprocessing. These processes and the useful range of process conditionsare all well known in the art.

Preferred embodiments include those where a catalyst, preferably aplatinum catalyst is used. Preferred processes include dehydrogenationof a C₃-C₄ paraffin to an olefin, for example the Oleflex® process, ordehydrocyclization of a paraffin feed containing feed and C₆, C₇, and/orC₈ hydrocarbons to aromatics (for example, processes which producebenzene, toluene and/or xylenes) such as the Aromax® process. In onepreferred embodiment the method of removing reactive metal is applied toa metal-coated dehydrogenation reactor system having a major portion ofits furnace tubes and reactor surfaces coated with said coating metal,preferably with tin.

The present invention is especially applicable to hydrocarbon conversionprocesses which require catalysts, especially halided catalysts, havingnoble metals such as Pt, Pd, Rh, Ir, Ru, Os, particularly Pt containingcatalysts. These metals are usually provided on a support, for example,on carbon, on a refractory oxide support, such as silica, alumina,chlorided alumina or on a molecular sieve or zeolite. Preferredcatalytic processes are those utilizing platinum on alumina, Pt/Sn onalumina and Pt/Re on chlorided alumina; noble metal Group VIII catalystssupported on a zeolite such as Pt, Pt/Sn and Pt/Re on zeolites,including L-type zeolites, ZSM-5, SSZ-25, SAPO's, silicalite and beta.

Examples of such processes include catalytic reforming and/ordehydrocyclization processes, such as those described in U.S. Pat. No.4,456,527 to Buss et al. and U.S. Pat. No. 3,415,737 to Kluksdahl;catalytic hydrocarbon isomerization processes such as those described inU.S. Pat. No. 5,166,112 to Holtermann; and catalytichydrogenation/dehydrogenation processes.

Metal-coated reactor systems are especially useful in processes operatedunder low sulfur conditions, since the coating provides improvedresistance to coking, carburization and metal dusting. This, in anespecially preferred embodiment of the invention, the hydrocarbonconversion process is conducted under conditions of “low sulfur”. Inthese low-sulfur systems, the feed will preferably contain less than 50ppm sulfur, more preferably, less than 20 ppm sulfur and most preferablyless than 10 ppm sulfur. In another preferred embodiment, the inventionis conducted under conditions of “ultra-low sulfur”. Here sulfur levelsare preferably below 100 ppb, more preferably below 50 ppb, and mostpreferably below 20 ppb S, with sulfur levels below 10 ppb andespecially below 5 ppb being particularly preferred.

One preferred embodiment of the invention involves the use of amedium-pore size or large-pore size zeolite catalyst including an alkalior alkaline earth metal and charged with one or more Group VIII metals.Most preferred is the embodiment where such a catalyst is used inreforming or dehydrocyclization of a paraffinic naphtha feed containingC₆, and/or C₈ hydrocarbons to produce aromatics, for example a C₆ to C₈UDEX raffinate. The invention is especially applicable to ultra-lowsulfur reforming using an intermediate or large pore zeolite catalystcontaining halogens, especially a halided platinum on non-acidicL-zeolite catalyst.

By “intermediate pore size” zeolite is meant a zeolite having aneffective pore aperture in the range of about 5 to 6.5 Angstroms whenthe zeolite is in the H-form. These zeolites allow hydrocarbons havingsome branching into the zeolitic void spaces and can differentiatebetween n-alkanes and slightly branched alkanes compared to largerbranched alkanes having, for example, quaternary carbon atoms. Usefulintermediate pore size zeolites include ZSM-5 described in U.S. Pat.Nos. 3,702,886 and 3,770,614; ZSM-11 described in U.S. Pat. No.3,709,979; ZSM-12 described in U.S. Pat. No. 3,832,449; ZSM-21 describedin U.S. Pat. No. 4,061,724; and silicalite described in U.S. Pat. No.4,061,724. Preferred zeolites are silicalite, ZSM-5, and ZSM-11. Apreferred Pt on zeolite catalyst is described in U.S. Pat. No. 4,347,394to Detz et al.

By “large-pore size zeolite” is meant a zeolite having an effective poreaperture of about 6 to 15 Angstroms. Preferred large pore zeolites whichare useful in the present invention include type L-zeolite, zeolite X,zeolite Y and faujasite. Zeolite Y is described in U.S. Pat. No.3,130,007 and Zeolite X is described in U.S. Pat. No. 2,882,244.Especially preferred zeolites have effective pore apertures between 7 to9 Angstroms. In a preferred embodiment, the invention uses a medium-poresize or large-pore size zeolite catalyst containing an alkali oralkaline earth metal and charged with one or more Group VIII metals.

The zeolitic catalysts used in the invention are charged with one ormore Group VIII metals, e.g., nickel, ruthenium, rhodium, palladium,iridium or platinum. Preferred Group VIII metals are iridium andparticularly platinum. If used, the preferred weight percent platinum inthe catalyst is between 0.1% and 5%. Group VIII metals can be introducedinto zeolites by synthesis, impregnation or exchange in an aqueoussolution of appropriate salt. When it is desired to introduce two GroupVIII metals into the zeolite, the operation may be carried outsimultaneously or sequentially.

Especially preferred catalysts for use in this invention are Group VIIImetals on large pore zeolites, such as L-zeolite catalysts containingPt, preferably Pt on non-acidic L-zeolite. Halided Pt L-zeolitecatalysts are particularly preferred. The composition of type L-zeoliteexpressed in terms of mole ratios of oxides, may be represented by thefollowing formula:

(0.9-1.3)M_(2/n)O:Al₂O₃(5.2-6.9)SiO₂:yH₂O

In the above formula M represents a cation, n represents the valence ofM, and y may be any value from 0 to about 9. Zeolite L, its x-raydiffraction pattern, its properties, and methods of preparation aredescribed in detail in, for example, U.S. Pat. No. 3,216,789, thecontents of which is hereby incorporated by reference. The actualformula may vary without changing the crystalline structure. Useful Pton L-zeolite catalysts also include those described in U.S. Pat. No.4,634,518 to Buss and Hughes, in U.S. Pat. No. 5,196,631 to Murakawa etal., in U.S. Pat. No. 4,593,133 to Wortel and in U.S. Pat. No. 4,648,960to Poeppelmeir et al., all of which are incorporated herein by referencein their entirety. Preferably, the catalyst be substantially free ofacidity.

In an especially preferred embodiment, the invention is a catalyticreforming method which uses a halided Pt L-zeolite catalyst. Prior tocatalyst loading and reforming, reactive metal is removed from atin-coated reforming reactor system. The process comprises:

a) removing reactive metal from a metal-coated reforming reactor systemby contacting the metal-coated reforming reactor with a getter toproduce movable metal;

b) sorbing the movable metal;

c) loading a halided Pt L-zeolite catalyst into the reactor system; and

d) reforming hydrocarbons to aromatics.

Preferably the mobile metal is sorbed onto a solid sorbent and thesorbent is located before the feed effluent heat exchanger.

In a more preferred embodiment the reforming process comprises:

a) coating a reforming reactor system with a tin-containing paint;

b) contacting the painted reactor system with a hydrogen-containing gasat 800-1150° F. to produce stannides;

c) removing reactive tin from said reforming reactor system bycontacting the reactor system with a gaseous stream containing HCl toproduce movable tin;

d) fixating the movable tin by adsorption onto a solid sorbent;

e) loading a halided Pt L-zeolite catalyst into the reactor system; and

f) catalytically reforming hydrocarbons to aromatics under ultra-lowsulfur reforming conditions of less than 10 ppb sulfur.

Thus, one preferred embodiment of the invention uses Pt L-zeolitecatalysts treated with halogen-containing compounds, referred to hereinas halided catalysts. These special types of catalysts have recentlybeen disclosed. For example, U.S. Pat. No. 5,091,351 to Murakawa et al.,discloses preparing a Pt L catalyst, and then treating it with ahalogen-containing compound. Other related patents that disclose halidedL-zeolite catalysts include EP 498,182 A which discloses co-impregnationwith NH₄Cl and NH₄F; U.S. Pat. Nos. 4,681,865, 4,761,512 and 5,073,652to Katsuno et al.; U.S. Pat. Nos. 5,196,631 and 5,260,238 to Murakawa etal. These catalysts also include spent catalysts that have beenrejuvenated by adding halogen-containing compounds (see, e.g., U.S. Pat.No. 5,260,238). These patents are all incorporated herein by reference.The halided catalysts described in these patents have been treated withhalogen-containing compounds, generally with chlorine-containing and/orfluorine-containing compounds. Preferably, the catalysts have beentreated with both chlorine and fluorine-containing compounds or with oneor more compounds containing both chlorine and fluorine. These halidedcatalysts have a desirably long catalyst life and activity. They areespecially useful for preparing aromatic hydrocarbons such as benzene,toluene and xylenes from C₆-C₈ aliphatic hydrocarbons.

We have observed that these halided catalysts evolve small amounts ofHCl and/or HF when these special types of catalysts are heated atelevated temperatures (e.g., at process conditions), or when contactedwith hydrogen at temperatures above about 300-400° F. And, this producedacid halide gas reacts with reactive metal present in metal-coatedreactor systems. Hence the need for the present invention. It should benoted that the above-described treatment with halogen-containingcompounds differs from that typically associated with platinum loading,e.g., by impregnation or ion exchange with compounds comprising platinumand halogen. This treatment also differs from that associated with washsolutions used during impregnation or ion exchange of conventionalcatalysts, where small amounts of halides may be added.

In some applications, for example in ultra-low sulfur reforming using anon-acidic Pt L-zeolite catalysts, it is preferred that the feed to thecatalyst be substantially free of sulfur, i.e. sulfur levels bemaintained at below 50 ppb, preferably below 10 ppb and more preferablybelow 5 ppb.

Preferred reforming process conditions include a temperature between 700and 1050° F., more preferably between 800 and 1025° F.; and a pressurebetween 0 and 400 psig, more preferably between 15 and 150 psig; arecycle hydrogen rate sufficient to yield a hydrogen to hydrocarbon moleratio for the feed to the reforming reaction zone between 0.1 and 20,more preferably between 0.5 and 10; and a liquid hourly space velocityfor the hydrocarbon feed over the reforming catalyst of between 0.1 and10, more preferably between 0.5 and 5.

To achieve the suitable reformer temperatures, it is often necessary toheat the furnace tubes to higher temperatures. These temperatures canoften range from 800 to 1250° F., usually from 850 and 1200° F., andmore often from 900 and 1150° F.

To obtain a more complete understanding of the present invention, thefollowing examples illustrating certain aspects of the invention are setforth. It should be understood, however, that the invention is notintended to be limited in any way to the specific details of theexamples.

EXAMPLE 1A Stanniding Steel Using a Tin Paint

Coupons of type 321 or type 347 stainless steel were coated with atin-containing paint. The paint consisted of a mixture of 2 partspowdered tin oxide, 2 parts finely powdered tin (1-5 microns), 1 partstannous neodecanoate in neodecanoic acid (20% Tin Tem-Cem manufacturedby Mooney Chemical Inc., Cleveland, Ohio which contained 20% tin asstannous neodecanoate) mixed with isopropanol, as described in WO92/15653. The coating was applied to the steel surface by painting andletting the paint dry in air. After drying, the painted steel wascontacted with flowing hydrogen at 1100° F. for 40 hr to produce astannided steel surface comprising intermetallics including ironstannides.

Some experiments were done in a pilot plant having a ¼″ OD reactor tubemade of 316 stainless steel. The reactor tube was coated with thetin-containing paint described above. The coating was applied to theinner surface of the pilot plant by filling the reactor tube with paintand letting the paint drain. After drying, the painted steel was curedwith flowing hydrogen at 1100° F. for 40 hr.

EXAMPLE 1B Analysis of Stannided Steel

The resulting tin coated steels with their intermetallic tin layers wereexamined visually for completeness of coating. Samples were mounted in aclear epoxy resin and then ground and polished in preparation foranalysis with the petrographic and scanning electron microscopes (SEM).EDX analysis can be used to determine the chemical composition of thelayers. The cross-sections of the materials showed that the tin painthad reduced to metallic tin under these conditions and formed acontinuous and adherent metallic (iron/nickel stannide) protective layeron the steel surface. Nickel- and iron-containing stannides were presentat a thickness of between about 2 to 5 microns. A nickel depletedunderlayer (2-5 microns thick) was also present. On the surface,microscopic tin balls and globules were observed.

EXAMPLE 2 Preparing a Halided Platinum L-Zeolite Catalyst

A halided platinum L-zeolite catalyst was prepared in a manner similarto EP 498,182A1, Example 4. Experiments showed that this catalystevolved HCl and HF when heated to 500° F. in the presence of hydrogen.FIG. 1 shows HCl evolution as a function of temperature. HF loss is alsoobserved. Gastec tubes were used to measure HCl concentration. Gas rateswere 1300 GHSV, once-through. Hydrogen was added at time=79 hours. Thiscatalyst was used for all the activity tests described below and as asource of HCl and HF in some of the following examples.

EXAMPLE 3 Stability of Stannided Coupon

A freshly-stannided coupon was prepared using the procedure described inExample 1. The coupon was weighed before stanniding. After stannidingthe coupon had increased 86.5 mg in weight. This coupon was placed in astainless steel pilot plant and was heated to 900° F. in a H₂/N₂mixture. After about 80 hr, the coupon was weighed again. It had lostless than 1 mg of weight. This example shows that in the absence of agetter (such as HCl), reactive tin does not readily migrate.

EXAMPLE 4 Comparative

A freshly-stannided coupon was prepared using the procedure described inExample 1. The coupon was weighed before stanniding. After stannidingthe coupon had increased 84.3 mg in weight. The stannided coupon wasplaced in a pilot plant and was heated to 1000° F. using a H₂/N₂ mixturecontaining 1000 ppm HCl. After 7 hours, the coupon had lost 40.3 mg ofweight. Assuming for calculation purposes that all this weight loss wastin loss, 48% of the tin was removed after 7 hr. After 22 hr, 87% of thetin had been removed.

This treatment procedure was too harsh; it removed too much of thestannide layer. The combination of temperature and HCl concentration wastoo aggressive.

EXAMPLE 5 Reforming Screening Tests

The impact of tin on catalyst performance was assessed in pilot planttests. Run 1 (144-181) was done in a type 316 stainless steel reactorthat was not stannided. One hundred and thirty cc of catalyst, preparedper Example 2, was loaded upstream of another catalyst layer of 60 cc.The set up shown in FIG. 2-1 was used. The catalyst served as an HCl/HFsource. A startup treatment of the catalyst was done. This startupincluded drying the catalyst in N₂ from room temperature to 500° F. for79 hr; then heating the catalyst in a mixture of 10% H₂ in N₂ from 500to 932° F. at a rate of 10° F./hr over a period of about 43 hr, and thenmaintaining the catalyst at about 932° F. for 24 hr. GHSV was maintainedat 1300 hr⁻¹ for the drying and reduction periods. Thereafter, theentire reactor was cooled to room temperature.

The upper catalyst layer was removed under a nitrogen blanket. Acatalyst performance test was done using the lower catalyst only. Testconditions were 100 psig, 1.6 LHSV, 3.0 H₂/hydrocarbon and a targetyield of 46.5 wt % aromatics. The feed was a C₆-C₈ UDEX raffinate froman aromatics extraction unit.

Run 2 (144-182) was set up as shown in FIG. 2-2. Here, afreshly-stannided reactor and freshly-stannided type 347 stainless steelcoupons were used. Because of the process configuration, the ratio ofstannided surface area to total catalyst volume was equal to about 20times that of commercial scale equipment. Eighty cc of catalyst preparedper Example 2 was loaded upstream of a stannided coupon prepared as inExample 1. Another catalyst layer of 80 cc was loaded downstream of thestannided coupons. Then the startup procedure of Run 1 was done. Aftercooling, the upper catalyst layer and the coupon were removed under anitrogen blanket. A catalyst performance test (as in Run 1) was doneusing the lower catalyst only. After the performance test, the lowercatalyst layer was analyzed and found to contain about 1,000 ppm tin.

After 1200 hours on stream, start-of-run (SOR) temperatures weredetermined for Runs 1 and 2 by extrapolating the line-out temperatureneeded to achieve the target aromatic yield back to time=0. SORtemperatures showed that the catalyst of Run 2 was about 10° F. lessactive than the catalyst of Run 1. It is believed that reactive tin hadreacted with evolving halides, including HCl, from the first catalystlayer, producing movable tin. This movable tin had deactivated thecatalyst in the second catalyst layer.

EXAMPLE 6 Catalyst Performance After Coupon Pre-Treatment

Pretreatment conditions were developed for removing reactive tin fromstannided coupons. A freshly-stannided coupon that had increased 77.5 mgin weight after stanniding was placed in a pilot plant. The coupon washeated to 900° F. using a H₂/N₂ mixture containing 100 ppm HCl. Movabletin was formed; it migrated downstream to the cooler portions of thepilot plant and plated out. The pilot plant was cooled at various timeintervals so that the coupon could be weighed. It was then reheated to900° F. After 7.5 hours, the coupon had lost 6.3% of the total tin (0.65mg/hr); after 13.5 hr, 9.0% (0.35 mg/hr); after 28.5 hours, 13.4% of thetin (0.23 mg/hr); after 44.5 hr, 16.5% (0.15 mg/hr); after 60.3 hr,18.8% (0.11 mg/hr). When these numbers were plotted (time versus wt %tin loss) The knee in the curve was observed at about 15 wt % tin loss.

The impact of a tin removal step prior to catalyst loading was assessedin a pilot plant test. Six stannided coupons were pretreated with 100ppm HCl at 900° F. Based on the above experiments, it was decided toremove about 15 wt % of the tin by pretreatment. It was estimated thatthis would take 40 hours. After 40 hours only 6-10 wt % of the tin hadbeen removed, so the coupons were heated again for an additional 20 hr.This process removed between 19-23 wt % of the added tin. These couponswere used in the following test, Run 4, below.

A separate pilot plant test, Run 3 (60-313), was set up as in FIG. 2-1with 80 cc of halided Pt L-zeolite catalyst in each bed. As in Run 1, astart-up procedure was done. This was followed by a catalyst performancetest using the lower catalyst only.

In Run 4 (60-314), the set up of FIG. 2-2 was used with a uncoated 316stainless steel reactor and with catalyst beds of 80 cc each. The sixtin-pretreated coupons described above were placed between the catalystbeds. The stannided surface area/catalyst volume in the second bed wasabout two times the stannided surface area/catalyst volume of a coatedcommercial reforming reactor system. After following the startupprocedures in Example 5, the coupons were weighed; they had lost anadditional 2-4 wt % of tin. A catalyst performance test using the lowercatalyst layer was done.

The catalyst performance in Run 4 was compared with Run 3. Performancetest conditions were similar to those in Runs 1 and 2, except that after500 hr, the severity was increased to 84 wt % aromatics. SORtemperatures showed that the catalyst of Run 3 had the same SORtemperature as the catalyst of Run 4. These results show that thereactive tin had been removed in the pretreatment process. The remainingstannide layer apparently did not react with evolving halides (HCland/or HF) from the first catalyst bed, so catalyst deactivation was notobserved in the second catalyst bed.

EXAMPLE 7 Multiple Startup Test

Multiple startup tests, using a fresh charge of catalyst each time, weredone in a stainless steel reactor that was not stannided. A halided PtL-zeolite catalyst (20 cc) was placed in the reactor andfreshly-stannided coupons of type 347 steel were prepared as in Example1 and cured at 1100° F. The weight gain associated with this stannidingwas measured. This gain was assumed to be 100% tin. These coupons and anuncoated type 347 stainless steel coupon were placed downstream of thecatalyst bed. The stannided coupons were weighed prior to testing. Thecatalyst and coupons were first dried in nitrogen at 1,300 GHSV. Thecatalyst was heated from room temperature to 500° F. at this flow rate.The coupons were kept at about 120° F. higher temperature than thecatalyst during the heat treatment. This simulated furnace temperaturesrelative to catalyst temperatures under commercial conditions.

Then hydrogen was introduced and the rate of nitrogen decreased, keepingthe total flow rate constant. The rate of hydrogen was maintained at 10%of the total flow. The catalyst was activated by treatment with thishydrogen in nitrogen stream (H₂/N₂=1/9) while the catalyst was heated ata rate of 10° F./hr from 500° F. to 932° F. over a period of about 43hours. Meanwhile, the coupons were heated at 10° F./hr from 60° F. toabout 1050° F. Afterwards, the catalyst was maintained at about 932° F.and the coupons at about 1050° F. for 24 hr in the absence of feed.

The reactor was then allowed to cool to room temperature in nitrogen andopened. After removing the catalyst, the coupons were removed andweighed. The coupons were then placed back into the reactor along with acharge of fresh catalyst. The heating procedure was repeated for asecond cycle. Additional cycles were done in the same manner.

FIG. 3 shows the results of this test. It shows the tin weight loss inthe coupons (e.g., wt % tin loss compared to the total tin added above)as a function of the number of start-up cycles. The bare, uncoatedcoupon did not show any weight loss (closed circles). As can be seen,the initial metal (tin) loss for the stannided coupon (open circles) washigh in the first cycle. In later cycles this weight loss decreased.Looking at FIG. 3, it can be seen that the original weight loss was 12wt % of the initial tin in the first cycle, 4 wt % in the second cycleand 2 wt % in the third cycle. This third cycle weight loss is about 10%of the initial weight loss rate (2% vs. 12%) and would be an appropriatetime to discontinue metal removal operations, as most of the reactivemetal has been removed.

EXAMPLE 8 Calculations for Commercial Scale Operations

The tin loss per unit area of coupons was calculated using the weightloss data from Example 7. Based on the tin loss per unit area, the totaltin loss expected in a commercial scale plant was calculated. It wasassumed that the total surface area in the reactors, furnace tubes andassociated piping would be covered by tin. Assuming all the lost tindeposits on the catalyst, the tin content of the catalysts and thecatalyst performance impact in a commercial unit were estimated. Theresults are shown below:

Estimated Tin Content of Commercial Catalyst and Performance ImpactIncremental Tin Deposit Estimated Catalyst Startup Cycle in Catalyst,ppm Activity Debit, ° F. (1) 1 800 8.0 2 250 2.5 3 150 1.5 4  50 0.5 5 50 0.5 Total 1300  13.0

This 13° F. start-of-run activity loss will significantly decrease runlength. Additionally impacts on catalyst stability could further shortencatalyst life.

EXAMPLE 9 A Large Scale Test

This example describes a large scale test and demonstrates a preferredembodiment of the invention.

A small, commercial scale, catalytic reformer is to be operated atultra-low sulfur reforming conditions using a platinum L-zeolitecatalyst with a C₆-C₈ UDEX raffinate feed. The sulfur content of thefeed contacting the catalyst is less than 5 ppb sulfur. The reactorsystem includes a sulfur converter/sulfur sorber, followed by fourreforming reactors, their associated furnaces and furnace tubes. Thereactors are made of 1¼ Cr, ½ Mo steel. The furnace tubes are made of304 stainless steel.

Prior to catalyst loading, the reactors, the furnace tubes and theassociated piping of the reactor system are treated with a reducible tinpaint. Several coupons are also placed in the reactor system. The paintis applied to the coupons and to all reactor system surfaces that are tocontact hydrocarbon feed at reforming or higher temperatures. The paintconsists of 1 part 20% Tin Ten-Cem (manufactured by Mooney ChemicalInc., Cleveland, Ohio), 2 parts powdered stannic oxide, 2 parts finelypowdered tin metal (1-5 microns in size) and isopropyl alcohol (forflowability). The Tin Ten-Cem contains 20% tin as stannous octanoate inoctanoic acid. After the paint is applied to a wet thickness of about 3mils, the coated reactor system is heated in a mixture of flowinghydrogen and nitrogen (1/9 ratio) for about 24 hours and then ismaintained at about 1050° F. for about 48 hours. It is then cooled toroom temperature. This procedure results in the painted surfaces beingstannided (with iron and nickel stannides). The tin migrates to coversmall regions (e.g., welds) which are not painted. The reactors andfurnace tubes are inspected, and any chunks of tin that that can bereadily removed are removed. The coupons are analyzed by petrographicmicroscopy; they show the presence of shiny microscopic tin balls.

Reactive tin is removed from this freshly-stannided reactive system. Abed of calcium on alumina is placed at the bottom of the last reactorand prior the effluent heat exchanger. A getter mixture consisting ofabout 1 volume % perchloroethylene (PERC) in hydrogen is passed over aPt on alumina catalyst at 900° F., to generate HCl in-situ. Theresulting gas is diluted with nitrogen to produce a gas containing 100ppm HCl which is passed into the freshly-stannided reactor systemdescribed above. The reactor system is heated to 600° F. over 6 hoursand then held at 600° F. until the reactive tin is converted to amovable form, believed to be tin chloride. The time at 600° F. isdetermined by using a set of freshly-stannided removable coupons ofknown tin content. When the reactive tin has been converted to stannouschloride, PERC addition is terminated. This is done by placing thecoupons in a vessel connected to the transfer piping located between thereactor and the furnace. Valves allow removal of the coupons foranalysis. A coupon is removed every ten hours, washed with water, driedand weighed. Weight percent tin loss vs time is plotted. This graph isused to determine when sufficient reactive tin is reacted and thus whento stop adding getter. Additionally, as the process nears completion,analysis using petrographic and electron microscopy shows that thestannided surfaces of the coupons are substantially free of microscopictin balls.

Thereafter, the reactor system is heated to 1000° F. in H₂/N₂ and thenis held at 1000° F. for 24 hours. The volatile SnCl₂ is fixated byadsorption onto the alumina sorbent in the last reactor. After thealumina sorbent is removed, the catalysts are loaded into the reactors.The halided platinum L-zeolite catalyst of Example 2 is used to reformthe raffinate feed to aromatics at temperatures between 800 and 1000° F.

The metals removal process is shown to be effective. The catalyst doesnot show any decline in activity as measured by SOR temperature comparedto what is expected for this catalyst in a non-stannided reactor system.

While the invention has been described above in terms of preferredembodiments, it is to be understood that variations and modificationsmay be used as will be appreciated by those skilled in the art. Indeed,there are many variations and modifications to the above embodimentswhich will be readily evident to those skilled in the art, and which areto be considered within the scope of the invention as defined by thefollowing claims.

We claim:
 1. A method for reducing catalyst contamination in ahydrocarbon conversion reactor system, comprising the steps of:contacting at least a portion of a metal-coated hydrocarbon conversionreactor system comprising a reactive metal with a getter to produce amovable metal; and fixating said movable metal.
 2. The method of claim 1wherein said fixating step comprises sorbing said movable metal.
 3. Themethod of claim 2 wherein said sorbing step comprises the step ofsorbing said movable metal using a liquid sorbent.
 4. The method ofclaim 2 wherein said fixating step comprises the step of washing saidmovable metal from the metal-coated hydrocarbon conversion reactorsystem.
 5. The method of claim 1 wherein said getter comprises a gaseoushalogen-containing compound.
 6. The method of claim 5 wherein saidgaseous halogen-containing compound is selected from the groupconsisting of organic halides, inorganic halides, a halided supportmaterial, and hydrogen halides.
 7. The method of claim 6 wherein saidgaseous halogen-containing compound comprises HCl.
 8. The method ofclaim 7 wherein said contacting step comprises the step of contacting atleast a portion of the metal-coated hydrocarbon conversion reactorsystem comprising the reactive metal with said getter comprising HClhaving a concentration between approximately 0.1 and 1000 ppm.
 9. Themethod of claim 8 wherein said concentration is between approximately 1and 500 ppm.
 10. The method of claim 9 wherein said concentration isbetween approximately 10 and 200 ppm.
 11. The method of claim 10 whereinsaid metal coating comprises tin.
 12. The method of claim 1 furthercomprising the step of removing said movable metal from the metal-coatedhydrocarbon conversion reactor system.